Hereinafter, this specification will describe prior art solutions derived from the side hung window but without limiting the scope of the invention to side-hung windows with traditional opening style, that is to say, with hinges configured to make the sash rotate about only one vertical axis.
Outward opening side-hung window units, usually made of metal, PVC or the like and of wood, are used for airing rooms and the parts of the windows inside the rooms are often equipped with accessories such as fly screens. In addition, to comply with safety regulations in the countries in which these window units are most widely used, these window units must have controlled opening with a limit on the angle achievable by the sash moving away from the fixed frame.
The window unit basically comprises:                a fixed frame;        a movable frame, or sash, usually connected to the fixed frame by        a pair of hinged arms interposed between the respective upper and lower rails of the two frames;        an operating unit located on the rail of the fixed frame and acting on the lower hinge or directly on the lower rail, allowing the sash to move away from the fixed frame (that is to say, controlled sash opening) and also allowing the sash to return in contact with the fixed frame;        an element for stably closing the sash on the fixed frame, the element usually being located on a fixed frame stile and acting on the respective sash stile (opposite that closest to the hinged arms) for stabilising closing.        
As can be seen in document U.S. Pat. No. 4,726,092 each of the above-mentioned hinged arms may comprise:                a support stably associated with the respective fixed frame rail and close to a fixed frame corner zone;        a first connecting arm hinged, at its ends, to the support and, respectively, to the end of a second arm which is associated with the sash lower rail to allow the opening and closing movements.        
The opposite, free end of the second arm is connected to a slide inserted in the support, which also allows the sash to slide along the two fixed frame rails, rendering sash opening a rotating—translating movement with the sash stile moved away from the fixed frame stile (an operation which may also allow improved access for cleaning the outer part of the glass from inside the room).
The operating unit or rotor, designed to control sash opening and closing, may comprise, normally and in prior art solutions as is also shown in documents U.S. Pat. No. 7,464,619 or CN 101131061, a housing unit for a control shaft, the unit being fixed on the outer edge of the fixed frame lower rail.
The control shaft has an inner portion equipped with a mechanism usually comprising helical toothing designed to mesh with a respective helical toothing or semi-toothing made around an operator arm pivot point inside the housing unit.
The operator arm is interposed between the lower rails of the fixed frame and the sash and is articulated, at its free end, to the sash rail.
The control shaft protrudes from the housing unit for connecting with a handle which is fixed or preferably applied by the user when necessary, thus allowing sash movement by manually turning the handle.
Obviously, the presence of the connecting point between the operator arm and the sash provides a low security closing seal, therefore, a second element is added, such as the above-mentioned stable closing element.
This element (also visible, in a prior art solution in document US 2008250719) substantially comprises a lock handle applied on the fixed frame stile and connected to a rod sliding along the inner part of the stile.
Therefore, the purpose of the rod is to form a connecting element between the sash and the fixed frame and it can usually be fitted with one or more strikers which, when the sash is closed, engage respective rollers or retaining elements present on the sash stile, resulting in stable closing of the window unit.
A window unit structured in that way has revealed disadvantages due to the separate structure of the operating and closing units.
As may be inferred from the above description, assembly of the operating unit requires complex machining on the outer profile (through-slots) of the fixed frame and, above all, machining also on the inner part of the fixed frame to allow the hinged arms and the operator arm to coexist. The presence of both necessitates machining on the thicknesses of the rails to render the window unit accessible for these operating elements (even in a superposed position).
Added to this is the need for machining on the window unit stiles (in particular through-slot openings) for allowing the insertion of the closing element.
Therefore, basically a window unit structured in that way is complex to make and so is expensive overall, as well as having complex operation as far as the user is concerned (obliged to go through various steps to open and close the window).